Magnetic resonance system and method for operating the same

ABSTRACT

In a magnetic resonance system and operating method, antenna elements in an antenna array are disposed around an examination volume, and each antenna element has a separate transmission channel and reception channel associated therewith. The magnetic resonance apparatus is operated to obtain magnetic resonance signals, from which amplitude and phase information are derived for the individual antenna elements, and this information is used to subsequently operate the antenna elements in the array to emit RF energy with a predetermined phase and amplitude so as to generate focused RF energy for hyperthermic treatment. The magnetic resonance apparatus can also be used to obtain magnetic resonance signals in intervals which during which the hyperthermic treatment is interrupted, from which the temperature of the region being treated can be ascertained.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a magnetic resonanceinstallation of the type having a basic field magnet, a number ofgradient field coils, an RF transmission and reception unit and acontrol unit for actuating the gradient field coils and the RFtransmission and reception unit for performing magnetic resonancemeasurements. The invention also relates to a method for operating sucha magnetic resonance installation.

[0003] 2. Description of the Prior Art

[0004] Magnetic resonance installations of the above general type areused in medical diagnosis in order to record images of the inside of apatient's body. Thus, magnetic resonance installations for imaging canbe used, for example, in neurology, angiography or cardiology.

[0005] A frequent field of application for magnetic resonance tomographyis the visualization or monitoring of tumors in cancer treatment. In thecase of a recent technique for handling such tumors, chemotherapy orradiation treatment is supported or replaced by targeted heating of thetumor-containing region by means of focused irradiation with radiofrequency (RF) energy. This recent technique is known by the termselective hyperthermia. With currently available hyperthermicappliances, the patient is positioned in a hyperthermic applicator, sothat the region of the body that is to be treated is arrangedapproximately in the center below the applicator. The hyperthermicapplicator is composed of a number of RF dipoles which are arranged inarray form and are each supplied with pulsed or continuous RF power ofdefined amplitude and phase. The phase and amplitude of the radiofrequency on each individual dipole are chosen such that the location ofthe region which is to be treated, i.e. of the tumor, is superimposedwith the RF energy radiated from the individual dipoles such that themaximum field strength is achieved at that point. Some of the focused RFenergy is absorbed by the tissue in the region of the tumor, so thatthis region is heated as a function of the radiated RF energy. Since thetumor-containing tissue is more heat sensitive than healthy tissue, theheating damages it to a greater extent than the surrounding healthytissue. Such targeted heat treatment can cause the tumor-containingtissue to die.

[0006] A fundamental problem in hyperthermic treatment is the differentpropagation speed of electromagnetic waves in the tissue and in thesurrounding air. Depending on the anatomy of the patient, thepropagation path of the electromagnetic waves from the transmissiondipoles to the tumor is filled by tissue or air to a greater or lesserextent. This influences the focusing, however, which means that it hasnot always been possible hitherto to focus the RF energy in optimumfashion during hyperthermic treatment without further auxiliary means.In the case of currently available hyperthermic appliances, the gapbetween the patient and the applicator is therefore filled with a watercushion which is filled with a special water solution after the patienthas been positioned. This water cushion approximately aligns thepropagation speeds of the RF radiation in the patient's body and betweenthe body and the hyperthermic applicator, so that sufficiently goodfocusing is achieved even for different patient anatomies. However, thisprocedure is an unpleasant experience particularly for claustrophobicpatients. In addition, simultaneous application of other applicators,for example for physiological monitoring of the patient during thehyperthermic treatment, is made more difficult by the water cushion,since little space remains for positioning additional applicators.

[0007] Hyperthermic treatment also requires the tissue temperature to bemonitored during the treatment. This is currently achieved using specialtemperature sensors which are mounted on catheters. During thetreatment, the catheters are inserted with the temperature sensorsthrough the patient's skin and are taken to the irradiated tissue. Thisinvasive method, however, puts an additional strain on the patient.

[0008] The search for improved techniques for recording the tissuetemperature during hyperthermic treatment also takes the use of magneticresonance measurements into consideration. The approach pursued in thiscontext involves determining the temperature by means of a magneticresonance examination which runs at the same time as the hyperthermictreatment. To this end, the hyperthermic applicator is placed in theexamination space of a magnetic resonance installation and a magneticresonance measurement is performed at the same time as the heating. Thetemperature of the tissue can be derived from the T1-T2 shift in themagnetic resonance signals obtained from the body region of interest.

[0009] One problem when applying a new approach to temperaturemeasurement is the accuracy of the temperature measurement. Thisaccuracy is currently barely sufficient, since the hyperthermicapplicator is arranged between the RF transmission and reception unit ofthe magnetic resonance installation and the patient, which means thatthe received signal from a magnetic resonance echo is received only veryweakly by the magnetic resonance installation's RF transmission andreception unit. In addition, the magnetic resonance signal is attenuatedby the water cushions arranged between the hyperthermic applicator andthe patient. Another cause of the insufficient accuracy of suchtemperature measurement is the choice of RF transmission frequency inthe magnetic resonance installation. These magnetic resonancefrequencies need to be sufficiently separated from the radio frequencyof the hyperthermic applicator in order to decouple the magneticresonance system from the hyperthermic system and to avoid mutualinterference by the two systems. Known hyperthermic applicators operatein the frequency range of 100 MHz in order to achieve sufficientfocusability for the radio frequency field in the patient's body. Forthis reason, the magnetic resonance frequencies are usually chosen in arange of 8-64 MHz in order to keep a sufficient separation from the 100MHz of the hyperthermic applicator. To excite the magnetic resonance,however, the chosen magnetic resonance frequencies require magneticfield strengths in the basic field magnet of between 0.2 T and 1.5 T. Atsuch basic field strengths, the temperature-dependent T1 T2 shift is notvery distinct, however, which means that this also impairs the accuracyof the temperature determination.

SUMMARY OF THE INVENTION

[0010] An object of the present invention is to provide an apparatus forselective hyperthermic treatment which allows sufficient focusing of theRF field without the use of water cushions and strain-free temperaturemeasurement with a high level of accuracy.

[0011] The above object is achieved in a magnetic resonanceinstallation, having in a known manner, a basic field magnet, a numberof gradient field coils, an RF transmission and reception unit and alsoa control unit for actuating the gradient field coils and the RFtransmission and reception unit for performing magnetic resonancemeasurements. In contrast to known magnetic resonance installations, theRF transmission and reception unit has multiple antennas that arearranged in array formed around an examination space and that can beactivated independently of one another using separate transmissionchannels for the purpose of emitting RF radiation of prescribable phaseand amplitude. For each of the antennas, a separate reception channel isprovided. The control unit, for each antenna, determines the amplitudeand phase of a locally selective magnetic resonance signal received bythe antenna and activates the antennas independently of one another forthe purpose of emitting RF radiation of prescribable phase and amplitudein order to generate an RF field focused in the examination space forhyperthermic treatment.

[0012] In the inventive method for operating the magnetic resonanceinstallation in the present case antennas and the gradient field coilsinitially are actuated for the purpose of performing a locally selectivemagnetic resonance measurement in the body which is to be examined. Themagnetic resonance signals are received with the antennas, and themagnetic resonance signals received from the body region which is to betreated are evaluated by the control unit for each individual receptionchannel, i.e. for each individual antenna, according to amplitude andphase in order to detect the amplitude attenuation and phase shift inthe radio frequency radiation on the path between the body region whichis to be treated and each individual antenna. Next, the individualantennas are actuated independently of one another by the control unitusing a suitable amplitude and phase and taking into account thedetected amplitude attenuation and phase shift, in order to generate acorrectly focused RF field for hyperthermic treatment at the location ofthe body region which is to be treated.

[0013] The present embodiment of the magnetic resonance installation andthe above-described operating method allow hyperthermic treatment of apatient without a water cushion. Actuation of each individual antennausing the correct amplitude and phase for the purpose of correctlyfocusing the RF field is ascertained in advance by detecting theamplitude and phase of the magnetic resonance signal received by eachindividual antenna from the body region which is to be treated. In thisway, regardless of the anatomy of the patient and the interspace betweenthe antennas and the patient, the correct amplitude and phase actuationis always achieved for optimum focusing of the RF field at the locationof a region which is to be treated, particularly a tumor. It is thuspossible to provide additional applicators, for example forphysiological monitoring of the patient during the hyperthermictreatment, while the same magnetic resonance installation can be used toperform a temperature measurement with a high level of accuracy andwithout any strain on the patient.

[0014] The present implementation of the magnetic resonance installationwith the simultaneous option of locally selective hyperthermic treatmentis achieved not by additional incorporation of a hyperthermic applicatorbut rather by simple redesign of existing components of a magneticresonance installation. In this context, the one or more powertransmitters for the antennas are designed such that they are firstlyable to deliver the continuous power required for hyperthermictreatment, which is in the order of magnitude of 1-2 kW. Secondly, thepower transmitters need to be designed such that they can deliversufficient pulsed power for magnetic resonance measurements, i.e. pulsedpowers in the order of magnitude of 20-30 kW. Preferably, this isachieved by replacing the customary pulsed power transmitters used inmagnetic resonance installations with a larger number of powertransmitters having a lower pulsed power per transmission channel.

[0015] The individual antennas are preferably in the form of resonancerods or elongate, electrically conductive material layers whose RFresponse is equivalent to that of resonance rods and which should havethe smallest possible dimensions. The individual resonator rods arearranged around the cylindrical space for the patient. They are alsoequipped with a matching device which matches the impedance of thetransmission path to the body region which is to be treated, whichimpedance is influenced by the patient and by the geometry in theexamination space, to the line impedance of the supply line whichconnects the respective power amplifier to the resonator rod. Thematching device can be equipped with a fixed transformation ratio or canbe oriented to each patient by means of individual tuning.

[0016] In one embodiment of the present magnetic resonance installation,a separate power transmitter is provided for each antenna. Each of thesepower transmitters is equipped with a separate transmitter actuationcircuit which allows phase control and amplitude control for theantenna. The actuation circuit should be able to generate any desired RFpulse shapes with widely differing pulse durations in order to allowboth the magnetic resonance measurements with pulsed excitement and thehyperthermic treatment with continuous irradiation. Each of thetransmitter actuation circuits preferably includes a modulator which issupplied from a discrete-value table via an analog/digital converter(ADC). The modulator can be in the form of an analog IQ modulator or adigital NCO. The frequency generation for the transmission frequency canbe effected using a PLL or DDS loop. Such circuits for frequencygeneration are known to the person skilled in the art in the field ofmagnetic resonance installations.

[0017] In the case of the present magnetic resonance installation, eachantenna also has a separate reception channel in order to be able todetect a magnetic resonance echo or signal which is induced in theantennas. To this end, the respective matching unit and the poweramplifier preferably have a transmission/reception changeover switcharranged between them which forwards the magnetic resonance signal oneach transmission antenna to a receiver circuit. The receiver circuititself is produced by a preamplifier circuit and a demodulator circuitwhich can separate each individual received signal according toamplitude and phase. The receiver circuit can be equipped with an analogIQ demodulator or with a digital demodulator. This receiver circuitallows detection of the phase shifts and of the attenuation of the RFamplitude in the tissue surrounding the tumor.

[0018] The present magnetic resonance installation is designed togenerate a sufficiently high magnetic resonance frequency which allowsexplicit focusing of the radio frequency field at the field strength ofthe basic field magnet. On the other hand, the field strength of thebasic field magnet is chosen such that an explicit representation of thetemperatures in the examined tissue is still achieved at the associatedmagnetic resonance frequency. For the field strength of the basic fieldmagnet, a field strength of 3 T is suitable, for example, which meansthat a magnetic resonance frequency of 123.2 MHz needs to be generated.This magnetic resonance frequency corresponds to a wavelength of 10-30cm in the patient's body and 2.5 m in the air, which means thatsufficiently intense focusing of the RF energy can be achieved.

[0019] The present magnetic resonance installation is preferablyoperated such that the irradiation with the RF energy to heat thedesired body region is repeatedly interrupted briefly in order toperform a magnetic resonance measurement for the purpose of ascertainingthe temperature in the body region in question. In this case, thetemperature measurement is performed using a conventional magneticresonance measurement with the antennas and subsequent evaluation of theT1-T2 shift. The local information is obtained in a known manner bymeans of the frequency and phase coding with the gradient field coils.

[0020] The temperature measurement is performed repeatedly in the courseof the heating process in order to be able to avoid overheating of theregion in question. The distances between the individual temperaturemeasurements are chosen according to radiated RF power, duration of theirradiation and the body region. Depending on the type of the magneticresonance measurement, i.e. according to the choice of pulse train, arange of a few 100 ms, particularly between 100 ms and 1 s, is providedfor the temperature measurement. Between the temperature measurements,the RF energy is radiated again in order to heat the body region whichis to be treated.

[0021] In one embodiment, a reception channel in the magnetic resonanceinstallation is connected to a surface coil which allows a very goodsignal-to-noise ratio for the magnetic resonance measurements fordetermining temperature. In this regard, a receiver circuit is providedin addition to the surface coils, which are designed in line with thereceiver circuits for the antennas of the RF transmission and receptionunit. In this embodiment, the antennas of the RF transmission andreception unit and the surface coils are additionally equipped with adetuning device in order to prevent any interfering influence on themeasurement by the currently unused part of the resonator. Such adetuning device is known from conventional magnetic resonanceinstallations.

[0022] For optimum focusing of the RF field when carrying out thehyperthermic treatment, information is required about the phase shiftsand the amplitude attenuation on the path from the individual antennasto the region of the patient's body which is to be treated, thisinformation being different for each patient on an individual basis. Toascertain this information, the invention provides, as already stated,for the magnetic resonance installation to be used before the start ofthe heating sequence to produce a tuning sequence in which the magneticresonance signals received from a prescribable body region are evaluatedin terms of their amplitude and phase received on individual antennas.In one embodiment, this tuning sequence is in the form of an FIDmeasurement, with suitable actuation of the gradient field coils beingable to prevent the emission of echoes from regions of the body whichare not of interest. Upon excitation, the tumor-containing regionradiates RF energy in the form of magnetic resonance signals which arethen intercepted by each antenna simultaneously. From a phase andamplitude differences, it is possible to derive the phases andamplitudes which are required for actuating the individual antennas inorder to generate focused RF radiation in the tumor-containing bodyregion. The antennas are then actuated using precisely these phases andamplitudes ascertained beforehand for each individual transmissionantenna.

[0023] Such a magnetic resonance measurement for ascertaining thecorrect phases and amplitudes for actuating the antennas can naturallyalso be repeated while the heating sequence is being carried out, byvirtue of said heating sequence being briefly interrupted for themagnetic resonance measurement. In this way, it is possible to attainoptimum focusing results even if the patient changes position during thetreatment.

DESCRIPTION OF THE DRAWINGS

[0024]FIG. 1 is a simplified illustration of the basic components of amagnetic resonance installation.

[0025]FIG. 2 schematically illustrates an exemplary embodiment of the RFtransmission and reception unit in a magnetic resonance installation inaccordance with the present invention.

[0026]FIG. 3 illustrates the superimposition of the RF fieldsrespectively generated by the individual antennas in a tumor-containingbody region of a patient, in accordance with the present invention.

[0027]FIG. 4 illustrates an example of the operation of an NCO forgenerating RF signals with correct amplitude and phase in accordancewith the present invention.

[0028]FIG. 5 shows an exemplary sequence for hyperthermic treatment,with simultaneous temperature measurement, in accordance with theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029]FIG. 1 shows a greatly simplified illustration of the basic designof a magnetic resonance installation in the form in which it is alsoproduced for the present invention. FIG. 1 shows the basic field magnet23, the gradient field coils 24, the RF transmission and reception unit25 which surrounds the examination space 27, and also a control unit 26for actuating the gradient field coils 24 and the RF transmission andreception unit 25. The units provided in magnetic resonanceinstallations, such as evaluation computer, memory, pulse sequencecontroller, pulse shape generator or RF generator, are combined in thecontrol unit 26 in this illustration.

[0030]FIG. 2 shows, as an example, an embodiment of an RF transmissionand reception unit in the form in which it is used in a magneticresonance installation based on the present invention. The RFtransmission and reception unit is made up of a multiplicity ofresonator rods 1 which are arranged in array form and are arrangedaround the cylindrical examination space 27 provided for the patient.Each of the individual resonator rods 1 is connected to a separatetransmission channel 2 and to a separate reception channel 3. The figureindicates just two of these reception and transmission channels for tworesonator rods by way of example. The transmission channel 2 comprises amemory 6 for storing the envelope and the phase profile for generatingthe RF excitation pulses. An NCO operated as a modulator 7 modulates thenecessary pulse shape and phase onto a carrier frequency signal f whichis obtained from a frequency generator (not shown). The signal is thenconverted in a digital/analog converter 8 and is amplified using thepower amplifier 9. The RF signal amplified in this way is supplied tothe resonator rod 1 via a tuning circuit 11 used for impedance matching.In this way, the individual resonator rods 1 are actuated independentlyof one another for the purpose of outputting RF radiation or RF pulsesof defined phase and amplitude. If the intention is to ascertain thephase and amplitude required for each individual resonator rod for thepurpose of focusing in a tumor-containing body region of a patient, thenthe individual resonator rods 1 are first actuated to output an RF pulsefor exciting a magnetic resonance excitation signal in this body region.Then, or else at the same time as transmission, actuation of gradientfields limits the physical region from which the FID signal is emittedto the tumor-containing region. Next, the transmission/receptionchangeover switch 10 is changed over in order to switch the resonatorrods 1 to reception or to connect them to the respective receptionchannel 3. The magnetic resonance signal is received by each of theresonator rods 1 and is supplied to an analog/digital converter 13 via apreamplifier 12. The digitized signal is split in an NCO 14, which isoperated as a demodulator, according to the phase and amplitude and issupplied to an evaluation computer 15 which evaluates the amplitude andphase of the magnetic resonance signal for a particular body region inorder to obtain for each of the resonator rods the amplitude and phasewhich is required for focusing. The individual resonator rods 1 are thenactuated using the amplitudes and phases ascertained for them in orderto achieve correct focusing in the tumor-containing body region. To thisend, the transmission/reception switches 10 are set to the transmissionchannel again and the individual resonator rods 1 have a continuous RFpower applied to them. This continuous power can also be composed of RFpulses.

[0031] This actuation with the correct phase and amplitude allows the RFenergy to be focused in the tumor-containing body region 16 of thepatient 17 without using water cushions, as indicated schematically inFIG. 3. To simplify matters, FIG. 3 indicates merely 6 resonator rods 1which are actuated using different phase differences Δδ and amplitudesΔ∪ in order to output RF radiation.

[0032]FIG. 2 also shows a way of measuring temperature during thehyperthermic treatment. For this temperature measurement, the heatingphase is briefly interrupted in order to generate an RF pulse using theresonator rods 1 for the purpose of exciting a magnetic resonancesignal. The associated pulse sequence is known to the person skilled inthe art from conventional magnetic resonance measurements. Optionally, asurface coil 4 can be positioned directly on the patient's body regionof interest and can be connected to a separate reception channel 5 forthe purpose of receiving the magnetic resonance signal. This receptionchannel 5, like the reception channels 3 for the resonator rods 1, has apreamplifier 12, an analog/digital converter 13 and an NCO 14 and isconnected to the evaluation computer 15. Measuring the resonance signalfor the temperature measurement using a surface coil has the advantageof a very good signal-to-noise ratio.

[0033]FIG. 4 shows an example of the interconnection of an NCO 7 as amodulator for the purpose of generating RF radiation of prescribableamplitude and phase. The NCO can also be operated in the oppositedirection in order to demodulate a received signal. As shown in FIG. 4,a register 19 as an output connected to an adder to which the incomingfrequency signal f(Δφ) is supplied. The output of the register 19 alsoserves as an input for a look-up table 18. The output of the look-uptable 18 is the sine (Re) and cosine (Im) data stream described below.

[0034] The digital data streams, which represent a sine and cosinesignal for the received RF signal in relation to a reference frequency,are generated in the same way as in the NCO, which is used fortransmission. Instead of the adder, the received data stream digitizedby the ADC is split over the two multipliers. One signal component ismultiplied by a sine data stream, and the other is multiplied by acosine data stream. When the two data streams have been subjected todigital low-pass filtering, the received RF signal is represented as areal-part component and an imaginary-part component in relation to thereference signal generated by the DDS (direct digital synthesis).

[0035] Finally, FIG. 5 shows a control sequence for actuating theresonator rods 1 for the hyperthermic treatment. In the top part, thetransmitted pulse 20 for heating the tissue can be seen. This heatingsequence 20 is briefly interrupted in order to radiate an RF pulse train21 for performing a magnetic resonance measurement in a known manner andthen to receive the magnetic resonance signal using the individualresonator rods 1 during a defined reception time 22. After that, heatingis continued with a fresh heating sequence 20. The bottom part of thefigure schematically shows the actuation pulses for the gradient fieldcoils for local coding in the x, y and z directions, as occur in thecase of a spin echo sequence. Other sequence techniques which are notshown in this case can naturally also be used for this purpose.

[0036] In the time interval for which the heating sequence is brieflyinterrupted, it is possible to derive the temperature of the tissue inthe body region of interest from the result of the magnetic resonancemeasurement.

[0037] The present system is able to implement all magnetic resonanceapplications which run at the radiated RF frequency. These applicationsare used in order to perform the anatomy representation or elsespectroscopic measurements in the patient's region of interest and tomeasure the temperature distribution in the patient. In addition, thepresent system is able to actuate the individual resonator rods suchthat targeted focusing of the RF field is possible. In this context, theheating sequence is split into time slots in order to be able tointerleave them with the magnetic resonance sequence for temperaturemeasurement, so that temperature measurement can take place more or lesssimultaneously with the heating.

[0038] In this context, the frequency at which the magnetic resonancemeasurements are performed is at least approximately equivalent to thefrequency at which the hyperthermic treatment takes place. This allowscorrect determination of the phase and amplitude with which eachindividual resonator rod needs to be actuated.

[0039] Although modifications and changes may be suggested by thoseskilled in the art, it is the invention of the inventor to embody withinthe patent warranted heron all changes and modifications as reasonablyand properly come within the scope of his contribution to the art.

I claim as my invention: 1-13. (Cancelled)
 14. A magnetic resonanceapparatus comprising: a basic field magnet that generates a basicmagnetic field in an examination volume; at least one gradient coil thatgenerates at least one gradient magnetic field in the examinationvolume; a plurality of radio-frequency antennas disposed in an arrayaround the examination volume for radiating RF energy into, andreceiving RF energy from, the examination volume; a plurality ofseparate transmission channels respectively connected to the pluralityof RF antennas; a plurality of separate reception channels respectivelyconnected to the plurality of RF antennas; and a control unit connectedto said at least one gradient coil and to said plurality of RF antennasfor operating said at least one gradient coil and said plurality of RFantennas to acquire magnetic resonance signals having an amplitude and aphase, from the subject, said control unit determining, for each antennain said plurality of RF antennas, the amplitude and the phase of themagnetic resonance signal received by that antenna, and said controlunit activating the antennas in said plurality of RF antennasindependently of each other to emit RF energy of a prescribed phase andamplitude into examination volume to generate an RF field focused in theexamination volume for hyperthermic treatment of the subject.
 15. Amagnetic resonance apparatus as claimed in claim 14 wherein each of saidseparate transmission channels comprises a power amplifier and amodulator.
 16. A magnetic resonance apparatus as claimed in claim 14wherein each antenna in said plurality of RF antennas is a resonatorrod.
 17. A magnetic resonance apparatus as claimed in claim 14 whereinsaid control unit interrupts generation of said focused RF field duringhyperthermic treatment of the subject at predetermined times for aninterval and, in said interval, activates said at least one gradientcoil and at least one antenna in said plurality of RF antennas foracquiring magnetic resonance signals indicating a temperature of aregion of the subject in which said focused RF field is present.
 18. Amagnetic resonance apparatus as claimed in claim 14 wherein said subjectin the examination volume has impedance characteristics associatedtherewith, and wherein said magnetic resonance apparatus comprises amatching circuit connected to said plurality of transmission channelsfor matching a line impedance of each transmission channel to saidimpedance characteristics.
 19. A magnetic resonance apparatus as claimedin claim 14 wherein said array comprises a cylindrical arrangement ofsaid plurality of RF antennas around said examination volume.
 20. Amagnetic resonance apparatus as claimed in claim 14 wherein said basicfield magnet generates said basic magnetic field with a field strengthof at least 2 T.
 21. A method for operating a magnetic resonanceapparatus comprising the steps of: operating a basic field magnet, atleast one gradient coil, and an RF antenna array comprised of aplurality of antenna elements, to radiate RF energy into, and to receiveresulting magnetic resonance signals from, a body region of a patientdisposed in an examination volume, said magnetic resonance signalscontaining location-dependent amplitude and phase information; from saidlocation-dependent amplitude and phase information, determining, foreach antenna element in the antenna array, an amplitude and a phaserequired for emitting RF energy from that antenna element to producefocused RF energy from the array into the body region; and operating theindividual antenna elements of the antenna array respectively with thedetermined and amplitude and phase to emit said focused RF energy for ahyperthermia treatment in the body region.
 22. A method as claimed inclaim 21 comprising operating said at least one gradient coil and saidantenna array in an FID control sequence to generate said magneticresonance signals.
 23. A method as claimed in claim 21 comprisingrepeatedly interrupting, for respective intervals, emission of thefocused RF energy during the hyperthermic treatment and, in each of saidintervals, operating said at least one gradient coil and said antennaarray to obtain further magnetic resonance signals, and determining atemperature of the body region from said further magnetic resonancesignals.
 24. A method as claimed in claim 23 comprising detecting saidfurther magnetic resonance signals using surface coils.
 25. A method asclaimed in claim 21 comprising operating said antenna array to emit saidRF energy at a frequency for generating said magnetic resonance signals,and operating said antenna array to emit said focused RF energy, also atsaid frequency, for said hyperthermic treatment.
 26. A method as claimedin claim 21 comprising interrupting emission of said focused RF energyfrom said antenna array for an interval during said hyperthermictreatment and, in said interval, obtaining further magnetic resonancesignals from said body region containing updated amplitude and phaseinformation, and re-determining the respective amplitudes and phases forthe individual antennas of said array, for emitting said focused RFenergy, from said updated amplitudes and phases.